NEW YORK (Reuters Health) - Men who spend significant
amounts of time kneeling on the job are at great risk of
developing osteoarthritis of the knee, a new study published in
the American Journal of Industrial Medicine confirms.

While several studies have suggested that people working in
jobs that require spending time on one's knees, such as floor
laying, are prone to knee osteoarthritis, few have been able to
quantify the amount of time spent kneeling that actually
increases risk, Dr. Alfred Franzblau of The University of
Michigan School of Public Health in Ann Arbor and colleagues
note.

Franzblau and his team evaluated 1,970 people participating
in the Third National Health and Nutrition Examination Survey
for whom knee X-rays were available, limiting their analysis to
people who had been on their longest-held job for at least five
years.

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The researchers had five ergonomics experts rate
occupations based on how much time a worker would spend each
day sitting, standing, walking or running, carrying or lifting
loads greater than 22 pounds, kneeling, or working in a cramped
space. This information "allows us to better identify the
magnitude of the exposure that contributes to risk," Franzblau
told Reuters Health in an interview.

Men in occupations requiring the most kneeling were more
than three times as likely as those who spent the least time on
their knees to develop knee osteoarthritis, the researchers
found. Heavy lifting also nearly tripled knee osteoarthritis
risk for men. For women, spending more time standing during the
workday increased the risk of knee osteoarthritis.

Based on these findings, the researchers estimate that 21
percent of symptomatic knee osteoarthritis cases in men are due
to working in jobs that require kneeling for more than 14
percent of the workday. Thirty-one percent of men in the study
had jobs that met this description, including nursery or farm
work or construction trades.

While just 5 percent of women in the study had jobs that
required kneeling, 35 percent had jobs that required them to
stand for more than 30 percent of their work day, in activities
such as operating machines or working in sales, the researchers
note. This means about 19 percent of cases of symptomatic knee
osteoarthritis in women are due to working in such jobs.

"Our results indicate that modifications to work methods
are needed to reduce occupational risk of knee osteoarthritis,"
Franzblau and his colleagues conclude.